Azodicarbonamide fog inhibitors

ABSTRACT

Azodicarbonamides, preferably having the general formula WHEREIN R1, R2, R3 and R4 individually are hydrogen, alkyl, aryl, or heterocyclic groups, or wherein the pairs of groups R1 R2 or R3 - R4 represent atoms necessary to complete a heterocyclic ring, are effective fog-inhibitors for silver halide photographic emulsions.

O United States Patent 1151 3,655,391 Merli et a]. 1451 Apr. 11, 1972 AZODICARBONAMIDE FOG R f r nc s Cited INHIBITORS UNITED STATES PATENTS 1 Inventors: Met", i 2,988,545 6/1961 Hill ..260/192 b Pordsnone; Luigl Valbusa, V19 3,100,704 8/1963 C0165... ....96/l09 x Grammy Ferrama, 591/9119, both of Italy 3,128,187 4/1964 Sagal ..96/109 I 9 3,134,764 5/1964 Blout .....260/l92X [221 Ned 196 3,396,023 8/1968 Rees ..96/67 [21] Appl.No.: 868,908 3,396,028 8/1968 Humphlett ....96/ 109 3,499,761 3/ l 970 Binghamton.... ..96/665 RelatedU S Application Dam 3,505,308 4/1970 Smith ..260/192 [63] Continuation-impart of Ser. No. 856,485, Sept. 9, PrimaryExaminer-JohnT.Goolkasian l 969. Assistant Examiner-M. E. McCamish Attomey-Kinney, Alexander, Sell, Steldt and DeLal-lunt [30] Foreign Application Priority Data [57] ABSTRACT May 16, 1969 Italy ..37,ll8A/69 Azodicarbonamides, preferably having the general formula Aug. 1, 1969 Italy ....39,l54 A/69 RI 0 0 R1 Sept. 9, 1969 Italy ..39,648 A/69 9,66.,2 12, R1 R1 [52] U S Cl 96/10 9 l6 234 wherein R R R and R individually are hydrogen, alkyl, [5]] 1m CL 107/02 G03c H34 aryl, or heterocyclic groups, or wherein the pairs of groups [58] Fieid u I I 665,67 68 RrR or R -R represent atoms necessary to complete 260/553 a heterocyclic ring, are effective fog-inhibitors for silver halide photographic emulsions.

11 Claims, No Drawings AZODICARBONAMJDE FOG INHIBITORS This application is a continuation-in-part of pending United States application Ser. No. 856,485, filed Sept. 9, 1969.

This invention relates to compounds useful as anti-fog, antistain, and stabilizing agents for silver halide photographic emulsions. More particularly, this invention relates to silver halide photographic emulsions containing such compounds and to photographic elements prepared from such emulsions.

The silver metal which appears in unexposed areas of a silver halide photographic element upon development is commonly referred to as fog. Fog may often be traced to the action of certain emulsion components, to the composition or nature of the developer, to atmospheric oxidation, to aging, etc. The type of packaging used for photographic film may influence fog formation, as may the type of film support upon which a silver halide emulsion is coated. For example, a polyester supporting film is more likely to contribute to the presence of fog in an overlying emulsion layer than in a cellulose ester supporting film. The aging of silver halide emulsions at high temperatures and high humidities generally favors the formation of fog.

Although fog generally appears as a uniform darkening of an emulsion layer in a photographic element, such layers also often exhibit small areas in which the fogging is much greater or less than that of the surrounding areas. Such small areas commonly are referred to as sensitization or desensitization spots, or more simply, as black spots and white spots". There spots have often been traced to the presence in the emulsion layer (or in a layer adjacent thereto) of metal particles such as particles of iron, copper, tin, etc., or compounds thereof. Such particles in turn are generally traceable to the type of supporting film utilized (e.g., polyester) or to the general environment in which the photographic material had been prepared or utilized.

Reduction or elimination of both fog and the abovedescribed spotting" in silver halide emulsions is greatly desired.

It has now been found that fog and spotting" (both of which are hereinafter referred to collectively as fog) in a silver halide emulsion can be greatly inhibited by employing as a fog inhibitor an azodicarbonamide, preferably a compound of the general formula wherein R R R and R individually are hydrogen or an alkyl, aryl, or heterocyclic group, or wherein pairs of groups R R or R R represent atoms necessary to complete a heterocyclic ring. Alkyl" and aryl as used herein include substituted alkyl (e.g., alkoxyalkyl, hydroxyalkyl, aralkyl, etc.) and substituted aryl (e.g., alkaryl, arkoxyaryl, etc.) groups.

Accordingly, the invention in one aspect relates to a silver halide emulsion having contacted therewith an azodicarbonamide compound. In another aspect the invention relates to a photographic element having a silver halide emulsion layer and having an azodicarbonamide compound in fog-inhibiting association therewith (e.g., in a layer adjacent the emulsion layer). In another aspect the invention relates to a method for inhibiting fog in a silver halide photographic emulsion comprising contacting the emulsion with an azodicarbonamide. The invention in a further aspect relates to certain novel azodicarbonamide compounds capable of inhibiting fog in silver halide emulsions and having the formula wherein R=,, R R and R may be hydrogen and wherein at least one of R R R and R is an alkoxyalkyl, alkoxyaryl, hydroxyalkyl, haloaryl, allyl, heterocyclic or heterocyclicalkyl group.

Azodicarbonamide compounds as a class have been found capable of inhibiting the formation of fog in a silver halide photo-graphic emulsion when contacted therewith. By contacted as used herein is meant that the azodicarbonamide is placed in fog-inhibiting association with the emulsion. For example, the azodicarbonamide may be incorporated within the emulsion, or in an adjacent layer, or in various photographic processing (e.g., developer) baths or the like. It has been found that the selection of the R R, groups in the abovedescribed formula does not greatly vary the capacity of the compounds to inhibit fog, Examples of compounds representative of the various classes of substituted azodicarbonamides are as follows:

EXAMPLE 1 N,N' DIMETHYL-AZODICARBONAMIDE 17.4 g.(0.1 mol) of azodicarboxylic acid ethyl ester were dissolved in ml. of diethyl ether, and to this solution 6.5 g. (0.21 mol) of methylamine in a 33 percent ethanol solution were added. The reaction occurred at 320 F (0 C.) and was immediate. After washing with diethyl ether, 9.3 g. of raw material were recovered in the form of an orange-colored powder, from which 7.79 of long orange-colored needles having a melting point of 336.2 F. (169 C.) were obtained by crystallization from ethyl acetate.

Calculated Found Analysis: C7c 33.40 33.46

rm 5.56 5.66 N% 38.87 38.72

EXAMPLE 2 N ,N DlETHYL-AZODICARBONAMIDE Azodicarboxylic acid ethyl ester (26.1 g.) were dissolved in 200 ml. of diethyl ether and to this solution 13.5 of ethyl amine in a 33 percent ethanol solution were added, the temperature being maintained below 680 F. (20 C.). The product was filtered, washed with diethyl ether and dried under vacuum. Yellow crystals (19 g.) having a melting point of 273.2- 275.0 F. (134 135 C.) were recovered.

Calculated Found Analysis: C92 41.90 41.97

EXAMPLE 3 N,N DIPROPYL-AZODICARBONAMIDE needles having a melting point of 305.6 F. (152 C.) were obtained.

Calculated Found Analysis)? C9? 48.00 47.8]

HV: 8.02 813 N7: 28.05 28.06

EXAMPLE 4 N,N Dl 2 METHOXYETHYL- AZODICARBONAMIDE Calculated Found Analysis:

EXAMPLE 5 N,N DIALLY-AZODlCARBONAMIDE Allylamine (12.0 g; 0.21 mol) in three times its volume of diethyl ether, was added to 17.4 g (0.1 mol.) of azoclicarboxylic acid ethyl ester in 5 times its volume of diethyl ether at 32.0 F. (0 C.). The amide (14 g) separated out almost immediately. By crystallization from 300 mol. of ethyl acetate, 9.5 g of small, orange-colored needles having a melting point of 291.2 F. (1440 C.) were recovered.

Calculated Found Analysis: CZ 48.90 49.07

m 6.16 6.28 Na 28.55 28.77

EXAMPLE 6 N,N DIISOPROPYL- AZODICARBONAMIDE To 17.4 g. (0.1 mol.) of azodicarboxylic acid ethyl ester in 100 ml. of diethyl ether were added 12.4 g. (0.21 mol.) of isopropylamine in ml. of diethyl ether at 32.0 F. (0 C.). A yellow-colored product (5.3 g.) separated out from which, by crystallization from ethyl acetate, 2.5 g. of small, patle, orangecolored needles were obtained. By evaporation of the mother liquors, another crop of product having a melting point of 316.4 F. (158 C.) separated out, yielding 4.3 g. of total product.

Calculated Found Analysis; C71 48.00 47.80

EXAMPLE 7 N,N' DIBUTYL-AZODICARBONAMIDE Calculated Found Analysis: C7z 52.90 52.86

EXAMPLE 8 N,N Dl 2 ETHOXYETHYL- AZODICARBONAMIDE 18 g (0.21 mol) of 2 ethoxyethylamine in 50 ml. of diethyl ether were added dropwise to 17.4 g (0.1 mol) of azodicarboxylic acid ethyl ester in ml. of diethyl ether at 32 F. 0 C).

The solid which separated was washed with diethyl ether to provide 17.5 g of product. Crystallization from ethyl acetate yielded 12.5 g of small, orange-colored needles having a melting point of217.4 F. 103 C.).

Calculated Found Analysis: C; 46.20 45.68

EXAMPLE 9 N ,N -BlS-[( 2-PYRlDYL)MET1-1YL]- AZODICARBONAMIDE To 17.4 g (0.1 mol) of azodicarboxylic acid ethyl ester in 50 ml. of diethyl ether were added 21.8 g (0.21 mol) of amino-2- picoline in 25 ml. of diethyl ether at 32 F. (0 C.). The reaction was immediate and the amide which separated out at once was washed with diethyl ether to provide 23 g of a pinkcolored powder. By crystallization from 600 ml. of methanol and concentration of the mother liquors, 10 g of orange yellow crystals having a melting point of 334.4 F. 168 C.) were obtained Calculated Found Analysis: cw 56.35 55.87

NZc 28.15 27.90

EXAMPLE 10 N,N' D1 (3-PYR1DYLETHYL) AZODICARBONAMIDE To 9.5 g of azodicarboxylic acid ethyl ester in 100 ml. of diethyl ether, 10.8 g of 2-amino-3-picoline in 50 ml. of diethyl ether were added at a temperature lower than 20 C. The reaction was isothermal and the solid amide separated out at once. By crystallization from methanol, orange yellow crystals having a melting point of l64162 C. were obtained.

Calculated Found Analysis: C7: 56.35 5638 H9? 4.70 5.08 N9: 28. l 5 28.16

EXAMPLE l1 N,N' Dl (4-PYDIDYL METHYL) AZODICARBONAMIDE To 9.5 g of azodicarboxylic acid ethylester in 100 ml. of diethylether, 10.8 g of -amino-4-picoline in 50 ml. of ether were added at a temperature lower than 20 C. The reaction was isothermal and the solid amide separated out at once, then it was washed with diethylether. By crystallization from ethanol small orange crystals having a melting point of 15715 9 C. were obtained.

Calculated Found Analysis: C7t 56.25 56.31

H7r 4.7 4.99 N92 28.15 27.88

EXAMPLE l2 N,N' BIS (2-HYDROXYETHYL AZODICARBONAMIDE To 17.4 g (0.1 mol) of azodicarboxylic acid ethyl ester, dissolved in 100 ml. of diethyl ether were added 12.4 g (0.21 mol) of ethanolamine dissolved in a mixture of 25 ml. of 5 ethanol and 25 ml. ofdiethyl ether at 32 F (0 C).

The reaction occurred immediately and the amide (17 g) separated out and was crystallized from 350 ml. of methanol 9.5 g of small orange-colored needles having a melting point of 285.8 F 141 C) were recovered.

Calculated Found Analysis: CZ 35.83 35.35

EXAMPLE 13 N,N BIS (3-HYDROXYPROPYL) AZODICARBONAMIDE Calculated Found Analysis: C7r 41.30 41.23

EXAMPLE 14 N,N' DIPHENYL- AZODICARBONAMIDE To 8.1 g of hydrazodicarbonamide (prepared by pyrolysis of 4-phenylsemicarbazide suspended in 200 ml. of pyridine was added a solution of 5.5 g of N-bromo-succinimide dissolved in 100 ml. of pyridine at a temperature of 950 F (35.0 C). The solid dissolved slowly and the solution became dark red in color. After about two hours, the solution was vacuum filtered and the filtrate was quickly poured into two liters of ice water.. A fluffy red-colored solid separated out which was then filtered, washed with water and crystallized from 150 ml. of hot ethyl acetate. Red colored plates having a melting point of 347.0 350.6 F 175 177 C) were obtained.

EXAMPLE 15 N,N D1 M-CHLOROPHENYL- AZODICARBONAMIDE To 92.8 g of nitrochlorophenyl 4 semicarbazide dissolved in 1200 ml. of ethanol, 25.4 g of iodine were added portion wise at the boil. The mass was allowed to boil for half an hour and was filtered hot. The resulting whitish solid (hydrazo compound) was washed with hot water and dried under vacuum at a temperature of 132.8 F (56 C). To 6.8 g of the N,N-di-3- chlorophenylhydrazo dicarbonamide, suspended in ml. of pyridine was added dropwise at 45 -50 C 7.6 g of N-bromosuccinimide in m1. of pyridine. The resulting solution was poured into 1.5 liters of ice water and the orange-red colored precipitate which was obtained was washed with water and crystallized from 200 ml. of hot ethyl acetate.

Extremely thin, orange red-colored, needles were obtained which decomposed at 341 .6 345.2 F( 172 174 C).

300 ml. of pyridine, 17.8 g of N-bromo-succinimide dissolved in 200 ml. of pyridine were added dropwise at a temperature of 158.0 F (70 C). The resulting solution was poured into ice water, and the orange-red precipitate which formed was filtered, washed, dried, under vacuum at room temperature, and was crystallized from hot ethyl acetate. The resulting compound, in the form of small deeply orange-red-colored needles, decomposed at 341.6 347.0 F 172 175C).

Calculated Found Analysis: C91 64.76 65.19

EXAMPLE 17 N,N Dl- -p -METHOXYPHENYL- AZODICARBONAMIDE To 6.6 g of hydrazodicarbonamide (obtained by pyrolysis of paramethoxyphenyl-4-semicarbazide) suspended in 150 ml. of pyridine was added dropwise 7.2 g of N-bromo-succinimide in 100 ml. of pyridine. The resulting solution was poured into ice water, and the dark red precipitate which was formed was washed with water, dried under vacuum, and crystallized. from hot ethyl acetate. Dark-red colored needles, melting at 336.2 350.6 F 169 -177 C) were obtained.

Calculated Found Analysis: C7: 58.50 58.50

EXAMPLE l8 N,N'-Dl-(a-PYR1DYL) AZODICARBONAMIDE Equimolecular amounts of a -amino-pyridine and diethylazo-dicarboxylate was reacted, in alcohol solution, at a temperature not exceeding 59.0 F (15 C). After the completion of the reaction, the mass was allowed to stand undisturbed overnight and the product which separated out was collected by suction. A dark yellow powder melting at 350.6- 354.2F 177 179 C.) was obtained.

EXAMPLE l9 N,N DI (B -PYRIDYL) AZODICARBONAMIDE Equimolecular amounts of B -amino-pyridine and diethyl azodicarboxylate were reacted, in alcohol solution, at 500 59.0 F (10 15 C.). After the completion of the reaction,

the mass was allowed to stand undisturbed overnight and the product which separated out was collected by suction. By repeatedly extracting the product with hot alcohol and concentrating the liquid under vacuum, needle-like crystals were obtained having an M.p. of 327.2 F 164 C).

EXAMPLE 20 N,N' Dl -PYRIDYL) AZODICARBONAMIDE Equimolecular amounts of 'y -amino-pyridine and diethylazo-dicarboxylate were reacted in pyridine at 590 F C). The reaction was allowed to go to completion overnight at room temperature.

The reaction product was a crystalline, yellow-colored solid melting at 352.4 357.8 F (178- 181 C.).

EXAMPLE 21 N,N DI (7 -FURYL) AZODICARBONAMIDE 2.5 g of N ,N' -'y -furyl-hydrazodicarbonamide, obtained by reaction of 'y-isocyanofuran with anhydrous hydrazine in toluene, was suspended in 100 ml. of dry methylene chloride and oxidized with N-bromo-succinimide dissolved in pyridine at about 50F (45 C). The reaction proceeded for 3-5 hours. The reaction product remained in solution and the unreacted hydrazo compound was removed by filtration. The filtrate was washed in succession with water, 2 percent hydrochloric acid, again water, 2 percent sodium bicarbonate solution, and again with water, in order to remove the reaction by products.

The structure for N,N'-di-('y-furyl) azodicarbonamide was confirmed by infrared spectra analysis.

EXAMPLE 22 N,N'-BIS (Z-TETRAHYDROFURFURYL) To 19.2 g of azodicarboxylic acid ethyl ester in 150 ml. of diethyl ether were added, at a temperature below 10C, 20.2 g of tetrahydrofurfurylamine in 150 ml. of diethyl ether. An orange yellow solid amide separated out having a melting point of 100 104C. By crystallization from ethyl acetate, orange red crystals having a melting point of l04-107C were obtained.

Calculated Found Analysis: C; 50.65 50.73

EXAMPLE 23 N,N' Dl -TH1ENYL) AZODICARBONAMIDE EXAMPLE 24 N,N-DIMORPl-1OLINO- AZODICARBONAMIDE EXAMPLE 25 N,N- BIS [2-(N-MORPHOLlNO)ETl-1YL]- To 19.2 g of azodicarbonxylic acid ethyl ester in 200 ml. of diethyl ether, at a temperature below 20C., 25.2 g of N-2- aminoethyl-morpholine in cc of diethyl ether were added. An orange crystalline solid amide separated out having a melting point of 143 C. By crystallization from propanol, orange red crystals having a melting point of C were obtained.

Calculated Found Analysis: C% 49.15 47.69

EXAMPLE 26 N,l\" D1 -(N-P1PERIDlNYL) AZODICARBONAMIDE carom I cm-cm CH1 N'C-N=N'CN CH2 CH: CH1 cHz cHz 17.4 g (0.1 mol) of diethyl-azo-dicarboxylate dissolved in 100 ml. of ether were reacted 41.0 to 50.0 F. (5 10C.) with 17. Og (0.2 mol) of piperidine dissolved in 100 ml. of ether. The color of the solution changed from orange to red as the reaction proceeded. After 30 minutes the solution was concentrated to a volume of about 30 ml. Yellow-orange colored crystals were formed which exhibited a M.p. of 269.6 273.2F(l32-134C.).

EXAMPLE 27 N,N DICYCLOHEXYL- AZODICARBONAMIDE To 17.4 g of azodicarboxylic acid ethyl ester in 100 m1. of diethyl ether, 19.85 g of cyclohexylamine in 150 ml. of diethyl ether, at a temperature lower than 10C, were added. The reaction was isothermal and a yellow solid in form of powder separated out at once. The yellow solid washed with diethyl ether and a melting point of 187 190C. By crystallization from ethanol, orange yellow needles having a melting point of 201 203C were obtained.

Calculated Found Analysis: C% 60.00 60.06

HZ 8.54 8.66 N9; 19.98 19.99

The compounds of the present invention are useful for inhibiting fog in silver chloride, silver bromide and silver iodide emulsions and in emulsions comprising mixtures of these silver halides (such as, for example, silver bromoiodide emulsions). The silver halide emulsions of the present invention may include various synthetic polymer substitutes or supplements for gelatin as colloidal binders, for example, dextran, polyvinylalcohol, polyvinylpyrrolidone, partially hydrolized polyvinylacetate, polyethylacrylate, polymethylmethacrylate, polyamides, and the like.

The emulstions of the present invention can be chemically sensitized by ripening with naturally active gelatin, by the addition of such chemical sensitizers as, for example, thiosulfate, allyl thiourea, thiocyanates, thiosulfanates, etc. Sensitization can additionally be carried out by the use of noble metal salts, (e.g., gold salts). The emulsions of the present invention may contain spectral sensitizers (e.g., cyanine and merocyanine dyes, etc), couplers, surfactants, hardeners, stabilizers, antifoggants, plasticizers, anti-oxidizing atents, development accelerators, and in general may include any of the variety of various additives which commonly are used in the production of photographic silver halide emulsions. Any suitable support, such as polystyrene, polyester, cellulose acetate, polycarbonate, paper, glass, and the like, can be used for the photographic elements of the present invention. The azodicarbonamides of the present invention have been found especially effective in inhibiting the fog which commonly results from the use of a polyester (e.g., polyethylene terephthalate) support, or when unusually rapid processes for emulsion coating and drying are employed.

Incorporation of azodicarbonamides into silver halide emulsions is conveniently accomplished by adding the azodicarbonamides in solution to the emulsions at the time the emulsions are prepared. Although it is preferred to have the azodicarbonamide compounds incorporated into silver halide emulsion layers, fog and spot inhibition is obtained if the compounds are at least contacted with the silver halide as previously described. For example, fog-inhibiting amounts of the azodicarbonamide compounds may be placed in a layer adjacent a silver halide layer in a photographic element or may be employed in photographic processing solutions. The amounts of azodicarbonamide compound which may be effectively employed in a silver halide emulsion layer or in a layer or layers adjacent thereto may vary widely, and may be readily determined by routine experimentation. When employed in a silver halide photographic emulsion, it is preferred to use from O.l l millimoles of azodicarbonamide compound per mole of silver.

The efficient fog-inhibiting capacity of compounds of the present invention may be more readily appreciated by reference to the following illustrative examples:

sensitometer and developed for 3 minutes at 680 F. (20 C.) in a developer having the following composition:

5 Metal 3 g.

anhydrous sodium sulfide 50 g. hydroquinone 9 g. anhydrous sodium carbonate 50 g. potassium bromide 3 water to make 1000 ml. 10

Test results in terms of fog and relative sensitivity are reported in Table 1 below for fresh emulsions and for emulsions stored for 15 days at l22.0 F. (50 C.) and 50 percent R.H.

TABLE 1 15 days at l22.0 F.

C. and 50%) Fresh R.H.

Relative Relative sensitivity Fog sensitivity Fog 2 5 Azodicarbonamide mM./MA.:

EXAMPLE 29 One portion of a silver bromoiodide emulsion layer containing 2 mole percent of Agl and 98 mole percent of AgBr on a cellulose triacetate support was overcoated with a protective layer 1.5 p. thick having the following composition:

Gelatin I5 g. l07: saponin-water solution 5 ml. water to make 1000 ml.

A second portion of the emulsion layer was overcoated with a protective layer having the above composition which additionally contained 1 g of azodicarbonamide (added as a 0.5 g./l00 cc. solution in dimethylformamide). The two portions were exposed and were subdivided into further portions which were developed in the developer of Example 28 for 3 and 10 minutes, respectively, at 680 F. (20 C.)

Test results are reported in the following Table 2:

EXAMPLE 28 A high-sensitivity silver halide photographic emulsion containing 2.0 mole percent of Agl and 98 mole percent of AgBr was divided into four portions. One portion was spread, without further treatment, on a polyester support. Azodicarbonamide in dimethylformamide solvent (0.5 g/lOO cc.) was added in the amounts set forth in Table 1 to the other emulsion portions which were then spread on polyester supports.

The resulting photographic elements were then exposed in a 75 A high-sensitivity silver bromoiodide emulsion containing 1.5 mole percent of Ag] and 98.5 mole percent of AgBr was divided into portions to which were added various selected compounds of the present invention in an amount of 1.5 millemoles/mole Ag. Development in the developer of Example 28 was carried out at 680 F (20 C) for 3 and for 10 minutes, respectively.

The results are reported in the following Table 3:

TABLE 3 Fresh Aged days, 50 C. 50% RH.

Relative Fog Fog Relative Fog Fog Compound of Example sensitivity 3 min. 10 min. sensitivity 3 min. 10 min.

Control 100 0. 14 0. 51 02 0. 0. 60

Azodicarbonamid (0.5 g/100 cc.

dimethyliormamide solution) 78 0. 00 0.35 88 0. 15 0. 33 1 (0.5 g., 100 cc. ethanol solution 72 0. 06 0.30 82 0. 05 0. 23 3 (0.5 g./100 cc. water solution) 79 0. 08 0.31 86 0.08 0. 29 4 (0.5 g./100 cc. ethanol solution)- 80 0. 05 0.29 82 0. 06 0. 28 5 (0.5 g./l00 cc. water solution)-.. 90 0.06 0.30 93 0. 08 0.28 6 (0.5 g./100 cc. water solution)... 87 0. 0S 0. 33 88 0.10 0. 7 (0.5 g./l00 cc. ethanol solution). 87 0. 12 0.41 04 0.14 0. 8 (0.5 g./100 cc. Water solution)-.. 80 0. 08 0.29 89 0.08 0. 28 9 (0.5 g./100 co ethanol solution)" 37 0. 06 0. 29 77 0. 05 0. 31 12 (0.5 g./100 cc. water solution)" 90 0.08 0.37 90 0. 08 0. 43 13 (0.5 g./100 cc. water solution) 90 0.08 0.37 90 0. 08 0.13

EXAMPLE 31 To portions of an emulsion containing 1.75 mole percent of Agl and 98.25 mole percent of AgBr were added azodicarbonamide and N,N'-diethyl-azodicarbonamide. Sensitivity and fog were measured for both fresh samples and samples which has been aged for l5 days at 122.0 F. C.) and at percent of AgBr and 2 mole percent of Ag] was divided into several portions. One portion (control) was spread on a polyester support without further treatment. The other emulsion portions were coated on identical polyester supports after adding thereto solutions of selected representative compounds of the present invention. The resulting photographic 50 percent R.l-l. elements were then exposed in a sensitometer and developed The results are summarized in the following Table 4. for 90 seconds in the developer of Example 28. The results of TABLE 4 Aged 15 days at 50 C. and Fresh 50% RH.

mM./ Relative Relative Compound M. Ag. sensitivity Fog sensitivity Fog Control 100 0.24 100 0.43 Azodicarbonamide (0.5 g./100 cc. di-

methylformamide solution) 0.3 100 0.23 100 0.28 Do 0.5 90 0.22 no 0.2a Do 0.6 90 0.21 110 0.23 N,Ndiethylazodicarbonamide (0.5 g./

100 cc. ethanol solution) 0.3 110 0.20 110 0.36 Do 0.6 100 0. 20 110 0.32 D0 0.9 100 0. 19 100 0.32

EXAMPLE 32 To illustrate the inhibiting effect exerted by the subject sensitometric tests carried out, respectively, on fresh emulsions and on emulsions aged for 15 hours at 161 .6 F. (72 C.) and 30 percent R.H. are reported in Table 6.

TABLE 6 Relative Relative mM./ sensitivity, sensitivity. Fog, Fog. Compound of Example MAg. fresh aged fresh aged Control 100 100 0. 52 0. 00 14 (0.5 g./100 cc. ethanol solution 0. 5 99 104 0. 33 0. 37 15 (0.5 g./100 cc. ethanol solution). 0. 5 102 103 0. 39 0. 41 16 (0.5 g./100 cc. ethanol solution). 0. 5 102 103 0.37 0. 44 17 (0.25 g./100 cc. ethanol solution) 0.15 100 103 0. 34 0. 46

compounds on the formation of spots caused by the presence EXAMPLE 34 of metal particles, the following test was performed:

A high-sensitivity emulsion chemically ripened with gold thiosulfate and thiocyanate was divided in two portions A (control) and B. 0.5 millimoles of azodicarbonamide (0.5 g./l00 cc dimethylformamide solution/mole Ag) were added to part B. The two emulsions were spread on a polyester support which had previously been dusted with fine iron powder. After drying and without exposure, the two portions were developed as described in example 28. The ability of the compound to inhibit the formation of black and white spots was determined by counting the number of spots per unit area for three samples of each of the portions A and B.

The results are reported in the following Table 5.

A silver halide photographic emulsion containing 98 mole To portions of a silver halide photographic emulsion containing 1.5 mole percent of Agl and 98.5 mole percent of AgBr were added selected compounds of the present invention in the amounts and solvents given in Table 7. Each portion was then coated on a polyester support which had been pre-coated with a subbing layer of gelatin containing iron powder suspended therein. The resulting photographic elements were maintained in a cooled condition for 10 minutes before drying, and were subsequently processed for seconds in the developer of Example 28. Thereafter the black sensitization spots caused by the presence of the iron particles were counted. The results are reported in Table 7.

l3 l4 EXAMPLE 35 EXAMPLE 38 A silver halide photographic emulsion containing 98 mole Samples of a silver halide photographic emulsion which percent of AgBr and 2 percent of AgI, and characterized by a contained 98 mole percent of AgBr and 2.0 mole percent of high silver to gelatin ratio, was divided into several parts. One Agl and to which the solutions of compounds of Examples 24 of these was spread and cellulose triacetate without further 5 and 26 had been added (as in Example 37) were spread on a additions. The other parts were spread after adding thereto cellulose triacetate base which was subbed with a subbing solutions (0.5 g./l00 cc. l/2O N H 80 of the compounds of layer of gelatin containing suspended iron powder. The sam- Examples 18 and 19 in varying amounts. Samples of the emulples were kept chilled for minutes before drying, and were sions were then exposed in a sensitometer and tray-developed l 0 subsequently processed for 90 seconds in the developer of Exfor five minutes at 680 F. (20 C.) i h developer f E ample 28. Thereafter the black spots resulting from the pie 28. Table 8 reports the results of en itomet i tests presence of iron particles were counted. The results are given ried out on fresh emulsions and on emulsions which had been in Table 1 aged for 15 hours at 72 C. and percent R.H.

TABLE 8 Relative sensitivity(aged; Fog (aged: Relative sen- 15h;30% R.H. 15h; 30% sitivity, fresh 161.6 F. Fog. RH. 161.6 MmJM.Ag (72 0.)) fresh F. (72C.)) Compound 01 Example:

Control 100 100 0. 31 0. 32 18 0 1 100 100 0. 31 0.32 0 5 95 so 0.25 0.28 2 5 76 67 0.19 0.19 0 1 95 80 0.31 0.31 0 5 80 80 0.20 0.20

TABLE 11 EXAMPLE 36 Number of subbing layer black spots Example was repeated with portions of a similar emuld {E 1 M A withdiron D9170 sion which contained 98 mole percent AgBr and 2.0 mole per- 35 Compoun 0 a m g pow er cent Ag! and to which the compounds of Examples 21 and 23 Control got prfsentfln. had been added. Results are reported in Table 9. I mm 48 24 TABLE 0 Relative sensitivity Fog (aged: (aged; 15 h; 1511, 30% Relative 30 a R.H. RH. 161. sensitivity. 161.6 F. Fog, 6 F. (72 Compound 01 Example Mm./M.Ag fresh (72 C'.)) fresh 0.))

Control 100 100 0. 0. 57 21 (0.5 g./100 cc. ethanol solution 0. 1 30 110 0. 30 0.35 21 (0.5 g [100 cc. ethanol solution). 0. 5 63 97 0.26 0. 32 23 (1.0 g./100 cc. pyridine solution). 0.05 0. 36 0.38 23 (1.0 g./ cc. pyridine solution)..- 0. 1 50 68 0.31 0. 33

EXAMPLE 37 55 EXAMPLE 39 Example 35 was repeated with a similar emulsion which Example 35 was duplicated except that solutions of the contained 98 mole percent AgBr and 2.0 mole percent Agl compounds of Examples 10, 11, 22, 25 and 27 were emand to which the compounds of Examples 24 and 26 had been ployed. Each compound was dissolved in ethanol at a concenadded. Results are reported in Table 10. 60 tration of 0.5 g./100 cc. Results are reported in Table 12.

TABLE 10 Relative sensitivity Fog (aged: (aged; 15 h; 1511: 30% Relative 30% RH. RH. 161. sensitivity, 161.6 F. Fog, 6 F. (72 Compound 0! Example MmJMAg fresh (72 0.)) fresh 0.))

Control 100 100 0. 25 0. 2s 24 (0.5 g./100 cc. ethanol solutio 0 1 107 0.25 0. 26 24 (0.5 g./100 cc. ethanol solution) 0.6 93 105 0.16 0.16 24 (0.5 g./100 cc. ethanol solution 2. 5 57 61 0.09 0.09 26 (1.0 g./100 cc. pyridine solution) 0.1 100 100 0.23 0. 24 26 (0.1 g./100 cc. pyridine solutionvn 0 5 96 105 0.20 0. 19 26 (1.0 g./100 cc. pyridine solution) 2 5 74 76 0.10 0. 13

TABLE 12 R1 0 R;

II I Stored: 1511:3091, N-CN=NCN Fresh RH. 72 C. R3 R4 gompopnd of M A Relative Relative xamp e m [M g Sensmv Fog sensmmy Fog wherein R R R and R individually are hydrogen or an al- Control- 100 0.31 100 0.3 kyl, ar l or heterocyclic group or wherein the pairs of groups 0.0125 79 0.1, 81 0.20 11 0,025 79 Q29 85 (L28 R R or R R represent atoms necessary to complete a 0. 050 19 0.18 85 0.17 heterocyclic ring. 22 Q10 95 23 96 39 0 The photographic element of claim wherein said fog-in- 95 96 1 hibitor is contained in a layer ad acent said silver halide emul- 2. 50 68 0.11 68 0.11

sion layer. 25 0.5 89 0.18 89 0. 20 6. The photographic element of claim 4 wherein said fog-in- H Q10 100 a 22 89 Q 30 hibitor is incorporated within said emulsion layer.

0 7 89 18 7. The photographic element of claim 6 wherein said emulsion layer contains from about 0.1 to about 15 millimoles of said fog-inhibitor per mole of silver in said silver halide. What is claimed is:

R; O O

wherein R R R and R individually are hydrogen or an alkyl, aryl or heterocyclic group or wherein the pairs of groups R R or R R, represent atoms necessary to complete a heterocyclic ring.

4. A photographic element comprising a silver halide emulsion layer and, in fog-inhibiting association therewith, a fog-inhibitor of the formula 8. A photographic element comprising a silver halide emulsion layer and, in fog-inhibiting association therewith, an azodicarbonamide as a fog-inhibitor.

9. An azodicarbonamide fog-inhibitor of the formula UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,655,391 Dated April 11, 1972 'Inventor(s) Paoli Merli and Luigi Valbusa It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Page 1 after the heading "Inventors" and before the heading "Filed insert Assignee: Minnesota Mining and Manufacturing Company, St. Paul, Minnesota Column l, line 56, "l6 Ll62C." should be l6 ll65C.--;

Column 8, line 18, formula of Example 25,

" CH -CH 0 --CH 2 2 2 2 O N- should be O N- CHE-CH3 CHE-CH2 Signed and sealed this 28th day of November 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO'WSO (10439) USCOMM-DC 6O376-P69 U.S. GOVERNMENT PRINTING OFFICE I959 O-365334 

2. The emulsion of claim 1 having from about 0.1 to 15 millimoles of said compound per mole of silver in said silver halide.
 3. A silver halide photographic emulsion having contacted therewith as a fog-inhibitor a compound of the formula wherein R1, R2, R3 and R4 individually are hydrogen or an alkyl, aryl or heterocyclic group or wherein the pairs of groups R1 - R2 or R3 - R4 represent atoms necessary to complete a heterocyclic ring.
 4. A photographic element comprising a silver halide emulsion layer and, in fog-inhibiting association therewith, a fog-inhibitor of the formula wherein R1, R2, R3 and R4 individually are hydrogen or an alkyl, aryl or heterocyclic group or wherein the pairs of groups R1 - R2 or R3 - R4 represent atoms necessary to complete a heterocyclic ring.
 5. The photographic element of claim 4 wherein said fog-inhibitor is contained in a layer adjacent said silver halide emulsion layer.
 6. The photographic element of claim 4 wherein said fog-inhibitor is incorporated within said emulsion layer.
 7. The photographic element of claim 6 wherein said emulsion layer contains from about 0.1 to about 15 millimoles of said fog-inhibitor per mole of silver in said silver halide.
 8. A photographic element comprising a silver halide emulsion layer and, in fog-inhibiting association therewith, an azodicarbonamide as a fog-inhibitor.
 9. An azodicarbonamide fog-inhibitor of the formula wherein R5, R6, R7 and R8 may be hydrogen and wherein at least one of R5, R6, R7 and R8 is an alkoxyalkyl, alkoxyaryl, hydroxyalkyl, haloaryl, allyl, heterocyclic or heterocyclic-alkyl group.
 10. A photographic element comprising a polyester support, a silver halide emulsion layer and, in fog-inhibiting association with said silver halide emulsion layer, an azodicarbonamide as a fog-inhibitor.
 11. A method for inhibiting fog in a silver halide emulsion comprising contacting said emulsion with an azodicarbonamide compound. 